In this case we have :
A Manx airline (is there a separate registration body for the Isle of Man, as they have their own aircraft registration sequence ?), based in a place which is not part of the European Union.
A flight between two EU states, but operating away from the airline home base.
An aircraft belonging to an operator from a third EU state.
An aircraft type which, I believe, has never been on the registers of the UK or Ireland.
Two crew with different native languages.
I wonder whose insurance they were on, which country's law will apply to that insurance, and which AOC authority does the daily oversight of the operation.
Why you no read Manx2 is not an airline, no way zilch.
Regarding the rest we are all in EASA land now so technically we should be singing of the same hymn sheet. All EU a/c are required to have the insurance that the regulatory bodies decide is appropriate. Any EU operator can fly to any other EU country. Suffice to say Flightline BCN were authorised under Spanish CAA and the rest came under the IAA and CAA.